[fsp] Fix crash because of calling net::GetMimeTypeFromFile on UI thread.

chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc

Index: chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc
diff --git a/chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc b/chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc
index f4e457781b6d3eaaa4de5597f3fbf59ab3606692..3ee9bcad6301e7ec0834cd7d427e918bfc91b4ee 100644
--- a/chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc
+++ b/chrome/browser/extensions/api/file_handlers/mime_util_unittest.cc
@@ -76,6 +76,7 @@ TEST_F(FileHandlersMimeUtilTest, GetMimeTypeForLocalPath) {
         &profile_,
         base::FilePath::FromUTF8Unsafe(kJPEGExtensionFilePath),
         base::Bind(&OnMimeTypeResult, &result));
+    content::BrowserThread::GetBlockingPool()->FlushForTesting();
     base::RunLoop().RunUntilIdle();
     EXPECT_EQ("image/jpeg", result);
   }
@@ -86,6 +87,7 @@ TEST_F(FileHandlersMimeUtilTest, GetMimeTypeForLocalPath) {
         &profile_,
         base::FilePath::FromUTF8Unsafe(kJPEGExtensionUpperCaseFilePath),
         base::Bind(&OnMimeTypeResult, &result));
+    content::BrowserThread::GetBlockingPool()->FlushForTesting();
     base::RunLoop().RunUntilIdle();
     EXPECT_EQ("image/jpeg", result);
   }
@@ -95,8 +97,14 @@ TEST_F(FileHandlersMimeUtilTest, GetMimeTypeForLocalPath) {
     GetMimeTypeForLocalPath(&profile_,
                             html_mime_file_path_,
                             base::Bind(&OnMimeTypeResult, &result));
+
+    // Since there are two calls to the blocking pool, it has to be flushed
+    // twice.
     content::BrowserThread::GetBlockingPool()->FlushForTesting();
     base::RunLoop().RunUntilIdle();
+    content::BrowserThread::GetBlockingPool()->FlushForTesting();
+    base::RunLoop().RunUntilIdle();
+
     EXPECT_EQ("text/html", result);
   }
 }
@@ -117,8 +125,13 @@ TEST_F(FileHandlersMimeUtilTest, MimeTypeCollector_ForURLs) {
   std::vector<std::string> result;
   collector.CollectForURLs(urls, base::Bind(&OnMimeTypesCollected, &result));
 
-  content::BrowserThread::GetBlockingPool()->FlushForTesting();
-  base::RunLoop().RunUntilIdle();
+  // Each URL may do up to 2 calls to the blocking pool. Hence, we need to
+  // flush it at least 6 times. This is unelegant, but there seem to be no

[not at google - send to devlin, 2014/07/08 16:02:28]

inelegant

and indeed.

it would be nice if FlushForTesting returned whether anything was flushed but I
can't see any candidates. it's a pity that the blocking pools don't just use the
runloop for testing. is there a way to arrange that? any chance it magically
already happens? I presume not, otherwise (i < 2) condition would work.

[mtomasz, 2014/07/09 02:21:02]

I just found a utility function in drive code:
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/chr...

I think we could upstream and reuse also here. WDYT?

[not at google - send to devlin, 2014/07/09 02:38:20]

hey that would be good. how do you propose to reuse it?

[mtomasz, 2014/07/09 03:55:42]

We could move that code from test_util.h|cc to a newly created 
content/public/test/blocking_pool_runner.h|cc.

We could then call
RunBlockingPoolTasksUntilIdle() here, instead of the unelegant loop. I think we
could also reuse it in other places. In Chromium code FlushForTesting is often
called twice for the same reason.

https://code.google.com/p/chromium/codesearch#chromium/src/base/threading/seq...
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/ses...
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/ui/...
https://code.google.com/p/chromium/codesearch#chromium/src/components/nacl/br...

And possibly tens of other places.

If you are fine with it, I'd like to do it in a separate patch. WDYT?

[not at google - send to devlin, 2014/07/09 13:23:50]

sounds good.

+  // better way.
+  for (int i = 0; i < 6; ++i) {
+    content::BrowserThread::GetBlockingPool()->FlushForTesting();
+    base::RunLoop().RunUntilIdle();
+  }
 
   ASSERT_EQ(3u, result.size());
   EXPECT_EQ("image/jpeg", result[0]);
@@ -139,8 +152,10 @@ TEST_F(FileHandlersMimeUtilTest, MimeTypeCollector_ForLocalPaths) {
   collector.CollectForLocalPaths(local_paths,
                                  base::Bind(&OnMimeTypesCollected, &result));
 
-  content::BrowserThread::GetBlockingPool()->FlushForTesting();
-  base::RunLoop().RunUntilIdle();
+  for (int i = 0; i < 6; ++i) {
+    content::BrowserThread::GetBlockingPool()->FlushForTesting();
+    base::RunLoop().RunUntilIdle();
+  }
 
   ASSERT_EQ(3u, result.size());
   EXPECT_EQ("image/jpeg", result[0]);